The present invention relates to a hydrogen separation membrane that does not require the use of costly Pd metal, is of low cost, and has superior hydrogen gas separability. The present invention also relates to a sputtering target for forming such a hydrogen separation membrane and its manufacturing method.
In recent years, there is increasing demand for efficiently separating hydrogen in fuel cells and other items. Generally speaking, since hydrogen produced from fossil fuel or water contains various impurities due to its manufacturing method, it is necessary to perform purification upon separating such impurities in order to obtain high purity hydrogen.
As the purification method, the PSA (Pressure Swing Adsorption) method, membrane separation process, cryogenic distillation method, absorption method and the like may be used. Among the above, the membrane separation process employing a metallic membrane is the only process that is able to manufacture ultrahigh purity hydrogen, which can be put into practical application, at a high yield and with sufficient speed.
The material that is currently being used in the metallic membrane separation process is a Pd—Ag rolled foil using Pd metal, which is a part of the platinum group elements. This Pd—Ag metallic foil has a characteristic feature of selectively occluding hydrogen and is effective as a hydrogen separation material. Nevertheless, there is a problem in that it is extremely expensive in comparison to other materials, and entails a drawback in that the operational conditions are complicated due to hydrogen embrittlement at low temperatures.
In light of the above, numerous materials that do not contain costly Pd have been proposed in the past (refer to Non-Patent Document 1). In particular, there is indication that a Ni—Nb—Zr metallic glass alloy is effective (refer to Non-Patent Documents 2 and 3).
Although the ultrafine processing technique, in particular the deposition technique, is primarily used for forming a hydrogen gas separation membrane, since even the crystal grain boundary of the formed film will become a problem in ultrafine processing, demanded is a deposition method capable of forming a film without a crystal grain boundary; that is, an amorphous membrane or an equivalent film, upon forming a thin membrane.
Meanwhile, as methods of manufacturing bulk metallic glass, proposed are a water quenching method of obtaining virgulate metallic glass by quenching the molten metal enclosed in a silica tube, a method of performing arc melting and quenching with a water-cooled copper mould, a clamping casting method of obtaining metallic glass by melting metal on a copper mold and thereafter pressing this with a cope and quenching the product, a method of performing injection molding at high pressure and quenching this in a copper mold, and a method of manufacturing a metallic glass wire rod by solidifying molten metal on a rotating disk (for instance, refer to Non-Patent Document 4).
Nevertheless, since each of these manufacturing methods is a manufacturing method from molten metal and is subject to quenching, it is necessary to devise the apparatus to meet the quenching conditions, and there is a drawback in that the cost would be extremely high. Further, even when forming a thin membrane, there are limitations, and there is a problem in that it was only possible to form a thin membrane of up to 30 μm in the past.    [Non-Patent Document 1] “Developmental Status of PEFC Electrode, Separator and Hydrogen Separation Membrane Employing Metallic Glass”, Written by Naotsugu Meguro, Fuel Cells, Vol. 2, No. 2, 2003, Pages 13 to 17    [Non-Patent Document 2] “Hydrogen Permeation Characteristics of Ni—Nb—Zr Metallic Glass Alloy”, Written by Shinichi Yamaura (and 5 others) (680) The Japan Institute of Metals, Spring Convention Lecture Summary (2003), Page 346    [Non-Patent Document 3] Shinichi Yamaura (and 6 others) “Hydrogen Permeation Characteristics of Melt-Spun Ni—Nb—Zr Amorphous Alloy Membranes” Materials Transactions, Vol. 44, No. 9 (2003) pp. 1885-1890    [Non-Patent Document 4] Functional Material “Manufacturing Method of Bulk Metallic Glass”, June 2002 Edition, Vol. 22, No. 6, Pages 26 to 31